The present invention relates to supporting apparatus. More particularly, the present invention relates to precise position control devices using magnetic power. For example, such supporting apparatus can be used for microlithography instruments.
FIG. 11 illustrates a conventional magnetic levitation supporting apparatus. FIG. 11(a) is a first example of such conventional supporting apparatus. FIG. 11((b) is a second example of the conventional supporting apparatus.
In the first example, permanent magnets 103 and electromagnets 105 are secured on a stage 101. Permanent magnets 103 and irons 107 are secured on a table 112. A wafer 110 is mounted on the table 112. Permanent magnets 103 of the stage 101 and permanent magnets 103 of the table 112 repel each other, because of like magnetic poles facing each other. This force of repulsion levitates the table 112. A sensor (not shown) detects the height of the table 112. A controller (not shown) changes the electric current of the electro-magnets 105 based on the height detected by the sensor so as to maintain the table 112 at a desired height.
In the second example (FIG. 11b), permanent magnets 103, arms 109, and electromagnets 105 are secured on the stage 101. Permanent magnets 103 and irons 107 are secured on the table 112. A wafer 110 is mounted on the table 112. Permanent magnets 103 of the stage 101 and permanent magnets 103 of the table 112 attract each other, because of facing opposite magnetic poles. The resulting attractive force levitates the table 112. A sensor (not shown) detects the height of the table 112. A controller (not shown) changes the electric current of the electromagnets 105 based on the height detected by the sensor so as to maintain the table 112 at a desired height.
However, these conventional stages have some problems as follows.
First of all. it is difficult for the conventional first and second stages to maintain the height (Z direction) because the table 112 is only supported by the repulsive or attractive force constant between the permanent magnets 103.
Second, it is difficult to maintain the force relationship between the electromagnets 105 and the permanent magnets 103. That is, when the table 112 is moved up and down by the electromagnets 105, the distance between the table 112 and the stage 101 changes. Therefore, the distance between the permanent magnets 103 fixed thereto inevitably changes. Accordingly, the repulsive or attractive force of permanent magnets 103 also changes.
Third, it is necessary to consume a lot of electric current to support the table at a different .DELTA.z position with respect to maintaining the table 112 at a predetermined position. Therefore electric current consumption increases and the electromagnets 105 generate heat because the electric current flows constantly. The heat affects the stage 101 to adversely influence the precision of the height (position) of the table 112.